Wednesday, May 14, 2014

Lasers As Weapons

Do you recall, a while back, the Navy’s video of the “highly successful” laser anti-small craft demonstration?  You know, the one where a laser was focused on a boat’s outboard engine and eventually melted the engine cover?  The video didn’t say, but the impression was that the process took somewhere between several minutes and many minutes.

Have you ever seen a small boat approach at high speed?  Can you see the engine?  No, all you can see is the shiny, reflective bow bouncing up and down.  Depending on the sea state, the boat may actually vanish from sight, momentarily, as it plunges up and down.

Let’s briefly review what a laser is.  In incredibly simplified terms, a laser is a narrow, focused beam of light unlike a flashlight where the light spreads out from the source.  The focus allows the beam to transmit high levels of energy to a pinpoint spot thereby causing damage.  The amount of damage is a function of the intensity of the beam and the duration of contact between the beam and the target.  The laser, being light, travels at the speed of light, 186,000 miles per second, and, for all practical purposes, is an instantaneous event.  Like all light, a laser can be reflected by mirrors or shiny surfaces or attenuated (diminished) by dust and water in the atmosphere.

The Navy’s goal is to create a laser weapon.  We’ve all watched Star Wars and have a mental image of what a laser will do:  an instantaneous vaporizing beam of destruction.  I don’t know what the Navy’s ultimate goal is but presumably it’s along those lines.  Specifically, I suspect the Navy is interested in lasers as an anti-missile defense, in particular as an anti-ballistic missile defense.  Of course, in the shorter term, they may have a lesser goal such as blinding a person in a small boat or some such.

Despite the Navy’s PR claims of wild success with the laser demo film clip, it’s obvious that we’re many years, probably decades, away from anything approaching a Star Wars type laser weapon.  OK, that just means it will take a while longer, yet, right? 

Here, though, is the problem:  I think the potential for effective countermeasures far exceeds the potential for the laser as a weapon.  For example, something as simple as making the attacking missile shiny and reflective would negate the laser’s effect.  I could imagine other, equally simple countermeasures.  For instance, attaching a spinning cap over the missile’s nose would prevent the laser from focusing long enough in one spot to have an effect.  And so on …

That’s the technical problem and here is the consequence:  the cost of developing an effective laser weapon is going to be grossly, insanely greater than the cost of developing countermeasures.  With any foreseeable future laser technology, laser development is headed down a rabbit hole of runaway costs.  Consider that the Air Force recently terminated their airborne laser test bed after decades of work dating back to the 1970’s, as I recall.  I wonder what the cumulative cost of that effort was?  I remember reading Aviation Weekly articles about the Air Force’s laser and the prediction that a practical laser weapon was just a relatively few years away.  Now, several decades later, the Navy is suggesting that we’re just a relative few years away from an effective laser weapon.  Nothing’s changed despite decades of work.  This is just one of those technologies that isn’t going to come quickly to fruition. 

Now I’m absolutely not suggesting that we halt laser research;  quite the opposite.  It’s well worth pursuing but it should be as a pure research effort and only at a low level of funding.  Every dollar spent by the Navy on lasers is a dollar not spent on a practical, near-term weapon.  Building future laser (and rail gun) support capability into the ships we’re building today is pointless.  Lasers won’t be an effective weapon during the lifetime of the ship’s we’re building now.  On a related note, the Ford clearly incorporates laser or rail gun sponsons.

So, let’s enjoy our scifi movies and let’s fantasize about Star Wars lasers but let’s keep a realistic view of the state of the technology.  Building ships based on non-existent technology is what got us the LCS.  Let’s not repeat the mistake with lasers. 

6 comments:

  1. The problem with lasers is that it takes a lot of energy to power and a lot of cooling a single laser capable of burning through hull or missile. Even then, it usually takes a few seconds of dwell to physically burning through any threat. This causes the added difficulty of keeping it focused on target for that duration. It is easier to launch and guide a projectile or missile to the same effect.

    I think lasers are a going to be a practical soft kill countermeasure to optical and/or infrared seekers long before it becomes a hard kill device. As more and more missiles receive IR or dual band seekers, NULKAs and Chaff become useless singularly and a laser based optical seeker jammer becomes needed. But it is simply impractical to try to actually shoot down anything with a laswer.

    ReplyDelete
  2. totally agree.

    To me right now the laser weaponry is ;

    A) or use as a dazzler on ir system and IR missles or the guys in the RHIB's
    B) useful as small UAV protection, either as hard kill or dazzler again.

    Its advantage is Ammo and cost of ammo, and right now, thats about it.

    Pity, and not necessarily a reason to stop research. But I too am fed up with people on defence site touting this as if its the answer to all woes. Its clearly a million miles of replacing even phalanx.

    Beno

    ReplyDelete
  3. Good points. And you'd think lasers would work quite well in the upper atmosphere where the Air Force operates, whereas the Navy operates in foggy places quite unlike the upper atmosphere.

    ReplyDelete
  4. The mirrors/shiny defense won't work against any laser that actually puts out some wattage. Mirrors are not perfect, and any light they don't reflect, which would be quite a bit, would be absorbed as heat. Considering the energy of combat lasers, mirrors would be vaporized quickly. The best defensive armor against a laser is something that absorbs a lot of heat.

    As for the atmosphere/fog/dust... "Even if only a small portion of the light is absorbed, high power beams can still significantly heat the air. Hot air will expand so that it reaches a lower density, leading to a core of lower density air through which the beam passes with higher density air outside. The gradient in air density acts like a weak lens that acts to defocus the beam. This defocusing due to heated air is called, Thermal Blooming."

    There are three main ways around blooming, the first being a large, curved mirror that refocuses the light downrange, avoiding high density most of the way. The problems with this in context of the navy is the size of the mirror, and the maneuverability of it.

    The second method is to use a very short pulse before the effects of blooming distort the laser. This means you would need a much more powerful laser to equal the loss of time on target.

    The third method is to simply have several low power lasers slaved to target a single point. Targeting would be interesting, along with finding the space for them.

    Part 1 of 2

    ReplyDelete
    Replies
    1. Part 2 of 2 (maybe)

      I am now going to go over some of the problems you might not have considered as far as ships are concerned. The main one being efficiency. Lasers are very inefficient, Ken Burnside describes weapon lasers as blast furnaces that produce coherent light as a byproduct. Free electron lasers have a maximum theoretical efficiency of 65%, while others are lucky to get half that. What this means is a 40% efficient 1 megawatt combat laser needs 2.5 megawatts of energy, the rest of it is nothing but waste heat, which could be a problem in a point defense system if you can only get so many shots off before your laser overheats. Efficiency will improve, but it will be subject to diminishing returns, like everything else.

      Another problem is that any laser defense could be overwhelmed same as our missile defenses, and unlike those, they can't defeat missile threats over the horizon.

      Lasers would be great for BMD installations, where size constraints don't matter. Or a ship designed solely for BMD with lasers.

      Delete
    2. My personal opinion is that megawatt-class free electron lasers (FEL) can be made to work in the way you have described, but that the ships which carry these large FEL's must be designed from the keel up to handle them. A truly effective FEL cannot be a bolt-on device, it must be an integral part of the warship's foundational architecture.

      IMHO, a large FEL that is being seriously stressed in a combat engagement will begin to consume its own mirrors. My proposed solution to that issue is to use a multi-mirror aiming turret and to build the FEL "laser gun tube" as a vertical shaft in the ship's superstructure surrounded by compartments which will allow direct access to the laser's critical components for change-out and replacement at sea, including the FEL's internal mirrors.

      While the Sailors of the Days of Yore (SOTDOY) had to lug cannonballs across their decks to serve their weapons, 21st-century sailors firing megawatt-class laser cannons will be pushing carts loaded with spare mirrors across their decks.

      Delete